The invention relates to a system and method for supplying a plurality of precise fluid volumes from a single syringe unit and more particularly this invention concerns the supplying of precise volumes of fluid by automatically selecting the desired plunger stop for each operation of the syringe device.
In many types of chemical analyzing systems it is desirable to provide a number of different fluid volumes in the system each of which precisely must be obtained. For example, in analyzing body fluids, sample volumes or aliquots are picked up and dispensed into reaction vessels in very precise volumetric amounts, generally with a precise amount of diluent. The tests in such a system may be monitored by measuring the chemical reaction resulting from the addition of one or more reagents to the sample and diluent volume.
For each of the tests selected for the body fluid of a particular patient, the amount of sample, diluent and reagent to be added for the test differ but each are alike from the point of view that the amounts selected must be extremely precise. For example, in one system in which the sample fluids and reagent fluids are picked up or aspirated by probes, the required test volumes using two different reagent probes and a single sample probe range from 2 to 500 microliters in increments of 2, 4, 6, 8, 10, 20, 40, 50, 60, 80, 100, 200, 400 and 500 microliters. It is apparent that it would be extremely desirable that each of the syringe units utilized in such a system have a wide range of flexibility as well as the capability of automatically selecting any one of the volumes to which it may be assigned to aspirate and dispense.
Further, since the sequence of testing in such a chemical analyzer will vary depending upon the number of tests to be conducted on the sample from each patient, as well as the number and type of tests the analyzer can perform, the syringe should be flexible so that any of the desired volumes may be selected during operation of the syringe. Further, since the results of the tests are related to the health of a particular patient it is extremely critical that the volumes selected accurately be obtained so that the test reaction correctly may be monitored.